Topic 7: Junctions Flashcards
what are the types of cell junction
- cell to cell anchoring junction (2)
- tight junction
- channel forming junction
- cell to matrix anchoring junction (2)
what are the types of cell to cell anchoring junction?
- desmosomes
- adherens junction
what are the types of cell matrix anchoring junction?
- hemidesmosomes
- actin linked cell matrix
what is the channel forming junction called?
gap junction
what are CAMs and what do thay do?
they are Cell Adhesion Molecules that are in discrete spots of the cell junction that
- recruit molecules that function in signalling pathways
- get linked to the cytoskeleton by the cytosolic domains’ adapter proteins
- they are like velcro at the tip of each junction
what is a hetrophilic CAM and what are some examples?
when the junctions attach to a different molecule on the other cell
- integrins and selectins
what is a homophilic CAM and what are some examples
who the cell junction must attach to the same molecule of the other cell
- cadherin and ig superfamily
what keeps embryonic tissues together?
classical cadherins
what is aheren?
it uses the transmembrane protein classical cadherins that is found in all animals and has over 180 members in humans
what is needed for classical cadherins to work?
they are calcium medicated, so if calcium os not present, adhesion can not occur?
what are the types of classical cadherins?
- E cadherins: epithelia
- N cadherins: neurons and heart
- P cadherins: placenta
- VE cadherins: endothelial cells
what is cell sorting and how does cadherins help enable it?
cell sorting occurs when cells in culture group themselves based on what type of cadherins they have and how much they have.
how does cell sorting organized when they have different level of the same cadherin?
the ones with the low level get pushed to the outskirt of the circle while the high levels are inside
how does cell sorting happen when they have different cadherins?
they organize in 2 operate groups, specifically P and E cadherins don’t like interacting with other cadherins
how does cell sorting and the changing of cadherins benefit a cell?
into embryonic stage, the sorting and changes in cadherins helps organize the cell so the tissues grow where they are suppose to be and grow new tissues like in epithelial to mesenchymal transition (EMT)
when are cadherins lost
in some tissue formation (eg EMT) or cancer progression
what is the strength of a typical caderin junction
the interaction of cadherins are homopilic and relatively weak BUT since there are multiple interactions all together it makes the junction strong
what is the protein constituents of a typical adheren?
the extracelluar space will have to identical cadherins bonded together but the intracellular space of the 2 cells may have different adapter proteins attaching to
- the alpha and beta catenin (the ones that attach the cadherin to the actin)
- vincluin
- p120 catenin
what do adherens (classical cadherins) attach to and what does desmosomes (non classical cadherins) attach to?
adherens attach to actin filaments while desmosomes attach to intermediate filaments
what is the function of adherens? (classical cadhereins)
mechanotransduction: they are dynamic tension sensors so they transduce a mechanical force ad modify the actin and myosin to balance the force
how do adherens assemble and what causes it?
1) when actin polymerization causes membrane protrusions, contact between the 2 cells begin
2) actin polymerization increases due to intracellular signalling, which causes more cadherin engagement
3) then myosin 2 generates tension with the actin which leads to the mechanotransduction
what do adherins do in epithelia tissue and what does it allow?
they couple the cytoskeleton of adjacent cells by forming a continue adhesion belt encircling all the interacting cells so the cells can undergo coordinated contraction
it allows invagination (removing portion of epthilea)
what is nectin and its structure and bind proteins
its a member of the IgG superfamily and first to get recruited in AJ
Structure: 3 IgG extracellular domains
Binding protiens: AF6/afadin
what is the 3 main differences between nectin and cadherin?
- nectin is calcium INDEPENDANT
- it can engage in homophile and heterophlic interaction
- a single nectin interaction has a higher affinity than cadherin
what are desmosomes and what is its function?
they use the non classical transmembrane proteins called desmoglein and desmocolin to link intermediate filaments
- specialized in strong adhesion (abundant in tissues with continuous mechanical force like the myocardium and epidermis)
what are the type of intermediate filaments desmosomes link?
it depends on the type of cell but for example
keratin in most epithelial cells
desmin filaments in heart muscle cells
what is the protein constituents of a typical desmosome?
- plakoglobin (y-catenin) most important
- plakophilin
- desmoplakin
what are hemidesmosomes and where are they found?
is a type of cell to matrix junction mostly found the basal junction
how do hemidesmosomes attach to the ECM and intracellular space
they attach to the extracellular matrix protein and intermediate filaments inside the cell
how do actin linked cell matrixes linked?
they attach to the actin filaments in the cell and the extracellular matrix proteins outside the cell
what is NCAM?
it is a ig superfamily CAM that is expressed on neural cell and express homophilic interaction while being calcium independent
what is ICAM?
it is a ig superfamily CAM that is expressed on endothelial cells and express heterophlic interaction while being calcium independent
- bins to integrins on white blood cells
what are selectin
they use lectins (calcium dependant carbohydrate binding protien) and recongize sugar on glycolipids and glycoproteins
what causes white blood cell recruitment (leukocytes)
B2 integrins: strong adhesion & emigration
selectin: weak adhesion and rolling
what are tight junction and where are they located?
cell to cell junction that are found apical to adheren junctions and maintain the polarity of epthilela cells by preventing diffusion of
- membrane proteins
- glycolipids
- macromolecules
- ions
- wate soluble molecules
paracellular pathway for he things that do get through
what is the structure of tight junctions
long branching network of homophile transmembrane protein called claudins and occludin?
what is the job of claudin and how is it determined?
permeability
by the size and charge of the extracelluar loop of the claudin
what is the job of occludin?
stability and permeability after it is built
how do tight junctions get connected to the cytoskeleton and what is its protien binding domain?
by zonula occludin (claudin and occludin) proteins to actin filaments
binding protein: PDZ & SH3 domain
what are gap junctions?
cell to cell junction that allow electric and metabolic activities through by flipping open and close
what are the transmembrane protien for gap junctions?
connexions (21 isoforms) and innexinshomo and hetrotypic isoforms
what are tunnelling nanotubes?
long thin membrane structures that span the distance of many cells to allow communication
example mitochondria and lysosomes use actin and microtules to travel along the TNT
however, they can get hijacked by viruses and cancer cells
